I saw the source code for a command line mp4 tag editor for Windows - it wouldn't compile in Puppy, but I could track it down again if someone with knowledge of C or something thought it would be useful.

Are there cli tools that you can use to view/edit tags in ape or m4a/mp4 formats?

The aac/m4a/mp4 formats apparently use conventional ID3 tags, so the id3lib utilities should (?) be compatible.

I have no experience with ape, but a Google search reveals that this format uses APEv2 tags -
http://en.wikipedia.org/wiki/APE_tag
A commandline tag utility for APEv2 is Apetag from
http://www.muth.org/Robert/Apetag/

Are there cli tools that you can use to view/edit tags in ape or m4a/mp4 formats?

The aac/m4a/mp4 formats apparently use conventional ID3 tags, so the id3lib utilities should (?) be compatible.

It might be worth looking at the faad2 package, but I also know that Easytag uses a cutdown version of libmp4v2, so that might be worth looking at._________________What's the ugliest part of your body?
Some say your nose
Some say your toes
But I think it's your mind

I tried to tag some m4a files I have with id3tag and they seemed to take but when I tried to play them with mplayer they are now unplayable. They played just fine before I tried to tag them. I'll try and figure something out though.

I did some more reading about MP4 tagging. ID3 metadata is definitely compatible, but there's some extra iTunes-related stuff in there as well. So any MP4 tagging applications problably need to be aware of this extra metadata, to avoid corrupting it.

As Dougal mentioned, Easytag can be compiled with AAC support using libmp4v2 as a dependency ... but Jason probably wants only the backend components.
The MPEG4IP project provides this libmp4v2 library, plus various utilities including the commandline tagger "mp4tags".
http://mpeg4ip.sourceforge.net/index.php

Alternatively, there is "AtomicParsley" which seems to take the tagging concept a step further by modifying the iTunes asset identification.
http://atomicparsley.sourceforge.net/

Those m4a files that I tried to tag with id3tag and won't play in mplayer anymore, can't even be decoded by ffmpeg or faad2. Oh well, just test files. I did just compile AtomicParsley & Apetag so I'm going to see how well those programs work and then incorporate them into pmetatagger if they work.

I just added ape support via apetag. It's supposed to work with mpc files too so I'm going to try them as well. I'll have to modify the gui a bit to support m4a/mp4 files via AtomicParsley since itunes uses a lot of tagging fields. It'll probably be tabbed when m4a/mp4 filetypes are selected. When I finish that up, I'll add the features to Pcdripper too.

I just added an option to dump the existing tags via a button click. This will save all the tag information to the directory where your file is. The file will be "Your-audio-file".ptag. This file is a just a basic text file that can be opened read & edited if need be. You can then use that ptag file to tag a new file from within pmetatagger. I'll work out a command line option to use a ptag file on a specific audio file which will bypass the gui. This will be especially useful in an audio conversion program to dump the existing tag and re-use it for the newly encoded file.

Now to restructure the program so it dumps the tags before the gui starts. Should've done that to begin with but I didn't think of the importance until now. This way you can view & dump the tags in a standard and useable way from the command line.

This has a bugfix, loading a single file from within the gui was broken, now fixed. I also added the dump tag information as noted above, and incorporated some new command line only techniques to dump the tag and use it on a different file. For more info enter at the cli:

# pmetatagger --help

One of these days I'll start work on a new pawdioconverter that will save tags by using the pmetatagger command line switches.

I read that wavpack (.wv) & optimfrog (.ofr) files accept APEv2 tags so I'll experiment with that and add the filetypes to the gui if successful. I need to find a .wma tag editor. Currently in pcdripper I'm using ffmpeg as the encoder for that format and even though ffmpeg supposedly accepts:

-year
-title
-author
-copyright
-comment
-album
-track

It seems that mplayer only notices title and author for ffmpeg encoded wma's. I don't see a way to use ffmpeg to view/edit tags though.